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6.6.5 Drylands


Though drylands are less diverse than other ecosystems, they contain thousands of species that are highly adapted to the dryland environment yet often neglected in conservation efforts. Arid and semi-arid rangeland ecosystems have seasonal climatic extremes and unpredictable rainfall patterns, but dryland species have evolved to be highly resilient by recovering quickly from drought, fire and herbivore pressure. Desertification (also known as land degradation in drylands) is a worldwide phenomenon (see Section 8.4.2).


Dryland degradation has many causes, including human conflicts. Large amounts of waste, garbage and toxic material were dumped and burned in desert ecosystems due to the Islamic Republic of Iran-Iraq war (UNEP 2016f). Drought, overgrazing, overuse of groundwater and unsustainable agricultural practices impose additional pressures (O’Connor and Ford 2014; Southern Africa Development Community 2014), though the extent of human versus natural causes are often difficult to disentangle.


The degradation of semi-arid and arid landscapes reduces capacity in terms of freshwater supply and food production, decreases wild food availability, and presents a threat to emblematic species and genetic resources (Low ed. 2013). Desertification has a damaging effect on soil health and vegetation, leading to adverse impacts that cascade through the food chain (Assan, Caminade and Obeng 2009). Salinization, mostly due to unsustainable irrigation systems, irrigated areas with poor drainage and poor quality of irrigation water, is a major problem in arid and semi-arid regions (see Section 9.5.6). The almost complete desiccation of the Aral Sea has led to the creation of the Aral Kum desert, which has caused degradation of riparian forests, pastures and other vegetation cover (Kulmatov 2008).


6.6.6 Forests


Forests provide habitat for large numbers of animal and plant species, and deforestation is one of the top threats to species diversity (FAO 2015b; Alroy 2017). Deforestation and forest degradation continue in many regions, often in response to demands for biomass as well as drivers outside the forest sector, such as urban expansion and agriculture, energy, mining and transportation development (see Section 8.4.2). Recent estimates show that tree cover loss is high across all forest types but differs across regions (Leadley et al. 2014). Tree cover density is associated with both losses and gains, but losses are especially high in the tropics and boreal forests; tropical rainforest accounted for 32 per cent of global tree cover loss over the period 2000-2012, with half of this loss occurring in South America (Hansen et al. 2013). Rates of forest gains approach or exceed rates of tree cover loss in some areas, particularly in temperate regions, reflecting forestry-dominated land management.


Recent work suggests that more biodiverse forests contribute a greater range of ecosystem services (Gamfeldt et al. 2013). Forests supply essential regulating services, including carbon sequestration, important for the regulation of climate, and protection of soil and water (Foley et al. 2007; Brockerhoff et al. 2017). With increasing deforestation and forest degradation,


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however, forest ecosystems can transform from net carbon sinks to carbon sources (Baccini et al. 2017).


The total number of people deriving benefits from forests — in the form of food, forest products, employment, and direct or indirect contributions to livelihoods and incomes — is estimated to be between 1 billion and 1.5 billion (Agrawal et al. 2013). In Africa, approximately 80 per cent of people are dependent on fuelwood (including charcoal) as their sole source of energy (UNEP 2016a, p. 76). Global exports of forest products were worth US$226 billion in 2015, with wood fuel comprising 9 million m3 m3


and industrial roundwood 122 million (FAO 2015b). Non-wood forest products, including wild


plant resources, typically contribute less to local economies, but can have high global market value. Contributions of forests to economies of the developing world are estimated at over US$250 billion (Agrawal et al. 2013). These economic benefits can only be maintained if forests are managed sustainably (FAO 2015a).


Though there are short-term employment gains from deforestation, the loss of forests translates into a loss of livelihoods: over 13 million people are employed in the formal forest sector, and another 40‐60 million people may be employed in informal small and medium-sized forest operations (Agrawal et al. 2013; FAO 2018c). A well-documented gender gap in access to forest resources suggests that poor management or loss of forest ecosystems may have different impacts on women and men (WWF 2013; Djoudi et al. 2015).


The direct health consequences of deforestation are complex: there is some evidence that forests can promote physical and mental well-being (Oh et al. 2017), while forest loss may increase exposure to infectious diseases, including malaria (Guerra, Snow and Hay 2006; Fornace et al. 2016) and other vector-borne parasites (Plowright et al. 2015; Hunt et al. 2017; Olivero et al. 2017).


6.6.7 Mountains


Mountain ranges cover around 22 per cent of the terrestrial space of the planet and provide multiple ecosystem services. At lower elevations, mountain habitats, especially those in tropical regions, are often more biodiverse and have higher levels of endemism than adjacent lowlands. However, habitat degradation and fragmentation has impacted many mountain ecosystems (Shrestha, Gautam and Bawa 2012; Chettri 2015; Venter et al. 2016) (see Section 4.3.2).


Mountain ecosystems are especially vulnerable to climate change: effects include shifts in species ranges and composition, with notable impacts on those organisms whose dispersal might be limited, or which are restricted to high altitudes, and local extinctions can occur for species in the upper margins of elevation gradients (Pauli et al. 2012; Khan et al. 2013; Grytnes et al. 2014; Knapp et al. 2017). Climate-induced warming can change ecosystem functioning, advance spring phrenology, and increase productivity and carbon uptake (Piao et al. 2012; Shen et al. 2016). Localised pressures include road construction, deforestation, mining, tourism, grazing of domestic livestock, burning and armed conflict (see Epple and Dunning 2014; Young 2014).


162 State of the Global Environment


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